April 19, 2017
Syringe Dispensed Solder Paste for Hand Soldering
You recently had a discussion about the application of liquid flux for hand soldering operations. Would you advise using a syringe to dispense solder paste as an alternative to dispensing flux only? If use of solder paste dispensed from a syringe was acceptable, what expiration would you apply to these syringes?
Solder pastes in syringes have lower viscosities and usually
lower metal content 80-85% compared to printable solder pastes which have 90+%,
separation is normally the issue.
The shelf life is less than liquid fluxes which have a 1 year
shelf life or more; solder pastes in syringes tend to be anywhere from 3 months
to 6 months and require refrigeration at 10 Centigrade.|
The usual issues with syringe dispensing are separation of flux
and metal in the syringe and/or needle blockage.
For liquid flux
applying flux in excess, is the issue. So both have advantages and
disadvantages in use.
Senior Market Development Engineer
Mr. Biocca was a chemist with many years experience in soldering technologies. He presented around the world in matters relating to process optimization and assembly. He was the author of many technical papers delivered globally. Mr. Biocca was a respected mentor in the electronics industry. He passed away in November, 2014.
I would only use a
syringe to dispense solder paste in applications where the volume of paste was
not critical, such as attachment of a metallic EMI shield. For component
leads, never. Solder paste for component mounting needs to be tightly
controlled, either by stencil printing or by jetting.|
In terms of
expiration, that depends a great deal on the paste chemistry. If you get
the syringe tubes from the paste manufacturer pre-loaded, then use the given
expiration date. If you are loading syringes yourself, work with your
vendor to determine how long a working life you have depending on how you fill
Principal Materials and Process Engineer
Doug Pauls has a bachelors in Chemistry & Physics, Carthage College, BSEE, Univ of Wisc Madison. He has 9 years working experience for US Navy - Materials Lab, Naval Avionics Center Indianapolis. 8 years Technical Director, Contamination Studies Laboratories. 11 years Rockwell Collins Advanced Operations Engineering.
Syringe-dispensed solder paste can be an acceptable substitute
for wire + liquid flux; some pastes work better than others for this
application. Many solder paste manufacturers sell "dispense grade" pastes that
have lower viscosity than pastes intended for stencil printing. If you
are not buying in the syringes but re-packaging from tubes, the shelf-life of
properly filled and stored syringes should be the same as for the original
packaging. Best practice is to label the re-packaged syringes with the
material, lot and date of expiry information from the original container.|
The key to success
with this process is controlling your dispensing operation and ensuring that
the flux is completely reacted. Hot air tools can be a good match for dispensed
solder paste; some pastes react badly to heating with an iron. Discuss your
intended soldering process with the solder paste manufacturer for guidance on
paste selection and process optimization.
Fritz's career in electronics manufacturing has included diverse engineering roles including PWB fabrication, thick film print & fire, SMT and wave/selective solder process engineering, and electronics materials development and marketing. Fritz's educational background is in mechanical engineering with an emphasis on materials science. Design of Experiments (DoE) techniques have been an area of independent study. Fritz has published over a dozen papers at various industry conferences.
Using syringe packed solder paste is a very common application
for SMT rework. Some of the key things to control in your facility:
Recycle the un-used
or partially used syringes according to the expiration date printed on the
- Keep the solder paste refrigerated until a couple of hours
before you plan to use it.
- Use ONLY solder paste that has been formulated for dispensing
- Use ONLY a tapered dispensing needle, this prevents solder paste
separation and reduces needle clogging.
- Set your dispenser at a low pressure, pressures over 35PSI can
cause the solder paste to separate.
- At the end of your day, recycle the needle and re-cap the
syringe. This protects the remaining solder paste in the tube.
Regional Sales Manager
OK International Inc.
Mr. Zamborsky serves as one of OK's technology advisers to the Product Development group. Ed has authored articles and papers on topics such as; Low Volume SMT Assembly, Solder Fume Extraction, SMT Rework, BGA Rework, Lead Free Hand Soldering, Lead Free Visual Inspection and Lead Free Array Rework.
paste can be a science in itself and in my opinion best to stay away from.
When dispensing solder paste the nozzle inside diameter (ID) size becomes
a big factor. If the nozzle is too small, the solder will separate in the
nozzle, so it is important to understand the relationship between particle size
of the solder paste and Nozzle dimensions.
Many solder company's
sale solder paste specifically designed for dispensing, so if this is something
you plan to follow up, you should make sure that your vendor understands that
you will be dispensing the material when discussing solder paste selection.
Dispensing grade solder paste will have higher flux content than standard
solder paste, this is by design to help lubricate the nozzle or dilute the
number of solder particles being forced out the nozzle at any given time,
reducing the number of opportunities to clog the nozzle.
Consult your vendor
for recommendations on shelf life for dispensing grade solder, typical solder
paste shelf life is around 6 months, however left at room temperature, the
metal in the solder paste will start to separate, so it is best practice to
dispose of unused material after a couple of days usage.
Global Marketing Director
Mr. Dixon has been in the electronics field for over twenty years and is the Global Marketing Director with the electronics group of Henkel. Prior to joining Henkel, he worked for Raytheon, Camalot Systems, and Universal Instruments.